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IAU Classifies Pluto & Eris As "Plutoids"

Posted by timothy on from the once-and-for-all-or-maybe-not dept.

Kligat writes "The International Astronomical Union has decided that Pluto and Eris should be classified as "plutoids," alongside their 2006 classification as dwarf planets. Under the definition, the self-gravity of a plutoid is enough for it to achieve a near-spherical shape, but not enough for it to clear its orbit of its rocky neighbors, and the plutoid orbits the Sun beyond Neptune." Reader FiReaNGeL links to a similar story at e! Science News.

11 of 192 comments (clear)

  1. Re:WTF is Eris? by MRe_nl · · Score: 5, Informative

    Eris, which measures about 70 miles wider than Pluto, is the farthest known object in the solar system at 9 billion miles away from sun. It is also the third brightest object located in the Kuiper belt, a disc of icy debris beyond the orbit of Neptune.

    --
    "Kill 'em all and let Root sort 'em out"
  2. Calimero by HetMes · · Score: 3, Informative

    It's a stupid debate altogether. I image all the astronomers involved feel really good about themselves for making an impact. Why couldn't they leave well enough alone? Pluto will always be the ninth planet to me, despite Eris. Definitions be damned!

    1. Re:Calimero by Cochonou · · Score: 4, Informative

      Classyfing Pluto as a Plutoid is not silly. Classifying Jupiter as a gas giant is not silly. Classying Mars as a telluric planet is not silly, either. This is exactly what you pointed out when you said that classifications were useful to catalog objects orbiting other stars.
      Now, what I think people are objecting to is the apparent lack of logic for the "planet" classification itself. You get objects as different as gas giants and telluric planets under the same umbrella, "planet". So, why not Kuiper belt objects ?
      But regardless of what has been the actual ruling about Pluto, the main problem lies in the redefinition process itself. What is a tomato, a fruit or a vegetable ? For biologists, it's a fruit, for cookers it's a vegetable. Everybody gets on with it. Different names for different fields, it's not uncommon. It has been going for ages.
      Now, what went through the mind of the IAU to think that the "planet" word needed a formal science definition ? The ambiguity of this word had been acknowledged for ages, and there was some disagreement among astronomers. They could just as well have kept on using accurate names, such as gas giants or kuiper belts objects. It's as if some day, the "International Biologists Union" decided it was a good time to formally define the word "bug". And ruled that only insects should be called bugs, and not arachnids.
      Anyway, it's not a big deal.

  3. Re:What about Ceres? by AstrumPreliator · · Score: 2, Informative

    I skimmed TFA and the release on the IAU's website. It looks as though they think Ceres is unique and so made the definition encompassing only trans-Neptunian dwarf planets. I'm not defending their reasoning, but that appears to be it.

  4. Re:WTF is Eris? by spacemandave · · Score: 5, Informative

    Eris, which measures about 70 miles wider than Pluto, is the farthest known object in the solar system at 9 billion miles away from sun. Eris is not the farthest known object in the solar system. It is a member of the "scattered disk," a subclass of Kuiper Belt objects (KBOs). It is the largest scattered disk object (SDO) discovered so far, but by no means the farthest away. This article has some nice diagrams that show the location of Eris relative to other known SDOs. There is another subclass of KBOs, called the "detached" objects, that are even further away. Sedna is a member of this family.
  5. Re:WTF is Eris? by spacemandave · · Score: 4, Informative

    IIRC it is a kuiper belt object that actually isn't on the same plane as the other planets. I think I actually recall it being found by accident because it isn't where we would expected it to be, most likely it is a captured object not formed by our suns accretion disk. It is unlikely that any of the Kuiper Belt objects were captured from somewhere else. The Kuiper Belt is thought to have formed from the same accretion disk that formed the planets. However, it is thought that the original Kuiper Belt contained far more material than it does today, and that the objects were in more circular and coplanar orbits than we find them today. Due to an episode of giant planet migration, this original disk was scattered and depleted.

    Many (but not all) of the observed dynamical features of the Kuiper Belt can be explained by giant planet migration.
  6. Re:Other solar systems? by uglydog · · Score: 2, Informative

    I was going to criticize your use of the word dickitry (it's been a slow day). I've heard of dickery, but not dickitry.
    Then I checked urbandictionary.com and was enlightened!
    dickery: the state of being a dick
    dickitry: The art of dicking around

    A subtle but very important distinction.

  7. Re:What a pantload by Abcd1234 · · Score: 2, Informative

    Yeah, I've long said the same thing about geologists classifying rock formations, or biologists classifying life forms...

  8. Re:I defy that classification, also refuse it by snuf23 · · Score: 2, Informative

    We call rocky planets also terrestrial or telluric. We call the other ones gas giants or jovian planets.

    --
    Sometimes my arms bend back.
  9. Re:Earth too by John+Meacham · · Score: 2, Informative

    There isn't any such limit. but it dillutes the usefulness of 'planet' as a term. This is astronomy, a science, it benefits from clear, precice, and _useful_ definitions. We can call everything that orbits the sun a planet if we like and lose its usefulness as a term, or we can just drop 'planet' as a scientific term and demote it to an historical anachronism. But neither of those are very good. If 'planet' is to be a useful term, it needs to have a precise and useful definition. There wasn't any such one that covered both pluto and the 8 planets. It's as simple as that.

    In a lot of ways science _is_ terminology. You can't think about things (in a critical scientific way) or talk about them or advance your understanding of them until you name them. When Maxwell's equations were originally formed, they required pages and pages of equations and could be understood only by top mathematicians of his time. Now we can write them in a few dozen characters and they are easily understood by advanced high school students. Why? Because we gave the concepts names, and symbols. As math advanced, we recogonized that vector spaces were useful enough to get their own terminology, making complex concepts simple. As we learn about the solar system, and astronomy, we also find that new things are useful and refine the old terminology.

    Of course, this is a fertile ground of discussion and there are various takes on the issues
      http://en.wikipedia.org/wiki/Philosophy_of_science

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    http://notanumber.net/
  10. Re:Because the discoverer of pluto by kalidasa · · Score: 2, Informative

    If the definition some of us preferred had been adopted, a certain Italian would have gotten his planet back, too.